Energy-saving techniques attract attention in such a point that electric energy for operating an air conditioner is minimized by suppressing a temperature rise due to entrance of thermal radiation energy of sunlight into a room through window glasses.
Generally, a laminated film in which a high refractive index layer and a low refractive index layer are made to have an equal optical film thickness and laminated alternately has a characteristic to reflect selectively light rays with respective specific wavelengths. Accordingly, as heat ray shielding films used for windows and components for vehicles, laminated films with selectively-reflecting properties to transmit visible light rays and to reflect selectively near infrared rays are utilized on a trial basis.
Hitherto, according to some of the reported film production techniques, laminated films are produced by laminating multiple layers through dry type film production methods, such as vacuum deposition methods and sputtering methods. However, the dry type film production methods have disadvantages such as high production cost, difficulty in enlarging an area of a film, and limitation of usable substrates to a heat-resistant material.
On the other hand, wet-type film production methods such as liquid coating methods have advantages such as low production cost and relative easiness in enlarging an area of a film. However, in the case where a laminated layer is produced by the wet-type film production methods, if the number of layers is too many, the industrial production of the laminated layer becomes difficult from the viewpoints of cost and difficulty in enlarging of an area.
According to another aspect, a capability to produce a flexible substrate such as a film is one of large features of the wet-type film production methods.
Conventionally, a coating film containing titanium oxides with a particle size of 100 nm or less and an organic silane compound as main components is proposed.
Further, conventionally, each of a high refractive index layer and a low refractive index layer is made to contain inorganic oxides. For example, it has been known to form an organic-inorganic hybrid film with a composition containing titanium oxide fine particles, an organosilicon compound, and a multifunctional acrylic compound as main components.
However, in the case where such a film is formed specifically on a base film, flexibility becomes insufficient and bending deformation and cracks tend to occur. In particular, in the case where such a film is to form an optical film with a refractive index difference and a good optical performance, since the content of hard inorganic oxides required to control a refractive index is forced to be increased, it is difficult to obtain a flexible film.
For example, Patent Document 1 discloses a film member containing a binder composed of rutile type titanium oxide particles and an organosilicon compound and air, and Patent Document 2 discloses a heat ray shielding film including a high refractive index layer composed of a resin layer containing inorganic particles. As a result of the evaluation conducted for the above films in terms of flexibility as the effect of the present invention, it turned out that the physical properties as a laminated film are not sufficient. In addition, above patent documents do not disclose the constitutions of the present invention.